Overhead HVAC Duct Heaters (DFF, DIF, DOF) Duct Heater

Caloritech™ HVAC Heaters come in three different series. DFF & DIF Series The Caloritech™ DFF & DIF Tubular Overhead HVAC Heaters are designed for operation with a primary HVAC system. The DFF comes with Finned tubular (Calrod® type*) elements while the DIF features Non-finned tubular (Calrod® type*) elements. The elements are positioned in a metal fabricated frame generally designed for removal during servicing without disturbing the heater frame. Elements are rigidly braced to minimize vibrations. DOF Series The Caloritech™ DOF Open Coil Overhead HVAC Heater is also designed for operation with a primary HVAC system. The unit is made from helical wound high grade nickel chromium resistant wires supported by interlocking ceramic insulators with four times the creepage distance between terminal and ground.


  • Available with finned and non finned tubular elements
  • Includes primary linear cutout on all units and secondary linear cutout on units under 300V and 30kW
  • Insert and flanged type construction available
  • Standard 16 gauge satin coated steel construction, special stainless steel construction also available

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DFF & DIF Series

Fully protected against mechanical shock, vibration or breakage
Completely encased resistance wire that will not sag, oxidize or deteriorate
Coiled alloy resistor wire is centered and permanently encased within highly compacted magnesium oxide, surrounded by a steel sheath

DFF Series Specific

Finned tubular (Calrod® type*) elements

DIF Series Specific

Non-finned tubular (Calrod® type*) elements

DOF Series Specific

Static pressure drop through open coil is very low, reducing fan horsepower requirements
Low element mass yields relatively small amounts of residual heat on fan shut down, reducing heat effect on surrounding material